Construction World February 2016

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Large POWER SYSTEMS symposium Hatch Goba presented a case study of a wind energy facility with high resistivity soil conditions at the joint CIGRE/IEC International Symposium on Large Power Systems in Cape Town last year.

This prestigious event was co-sponsored by Hatch Goba, together with other multinationals such as ABB, which was held under the theme of ‘Development of Electricity Infrastruc- ture in sub-Saharan Africa’. This is only the second time that the symposium has been held on the African continent, and the first of the new century. Symposia are held in odd-number years, in various countries where CIGRE is present, focusing on specific subjects of topical interest. The previous one took place in Cairo, Egypt in the 1980s. The Cape Town symposium was held over five days, comprising a full day of tutorials, three days of paper presentations in two parallel sessions, and a day of technical tours. The symposium was supplemented by an exhibition that included equipment manufacturers, suppliers, construction contractors and consultants in the power industry. >

Philip König, Hatch Goba, regional director, Africa, Europe and Middle East.

The Cape Town event attracted a record 400 delegates, from Africa, Australia, Europe and America. Paper submissions were scrutinised and adjudicated by an international review panel in Paris, with Hatch Goba having a successful submission entitled ‘Safe Groundmat Design for Grid Connection Substations at Wind Energy Facilities’. The paper was presented by Nitin Thekkumpuram, Hatch Goba, and co-authored by Philip König, Ron Coney and M. Khan. It focused on the location of wind energy facilities (WEF), which is often if mountainous terrain with rocky ground, resulting in high soil resistance values. The combination of high soil resistivity and a high fault current results in an unsafe potential rise within the wind farm area, and transfer of dangerous potential to metallic structures and underground services within the WEF. The paper from Hatch Goba presented a case study on how an inte- grated grounding system can prevent these unsafe conditions where soil resistivity is extremely high. This system was tailored for the specific site conditions encountered in the case study. The WEF in question consisted of 31 wind turbines spread across local community land, delivering a total output of 93 MW or 3 MW per wind turbine. The grind integration of the WEF required upgrading an existing upstream substation to 132 Kv, establishing a new 132/33 kV substation and the interconnecting powerline infrastructure between the substations. Each turbine in the WEF is connected to an underground collector strings, which are terminated at the medium voltage side of the new grid connection substation. The substation is equipped with two 132/33 kV 50 MVA transformers. THE WEF is located in an area with very high soil resistivity due to loamy and rocky soil conditions, which was confirmed by an investiga- tion. Using a bare copper earthing system would have resulted in very high potential gradients around the grid connection substation and unsafe touch potentials within the inhabited village area next to the substation. To mitigate this problem, a new approach of integrated earthing using insulated cables to connect the individual wind turbine ground- mats to the substation groundmat was introduced, taking into account the equivalent circuit of the whole WEF. CIGRE (the International Council on Large Electric Systems) allow engineers and specialists from all around the world to exchange informa- tion and enhance their knowledge related to power systems. Hatch Goba’s capabilities in this sector include wind assessments, feasibility studies, site research, engineering design services, project management, interconnection services, environmental assessment and permitting services, construction supervision and due diligence. Hatch Goba also integrates wind and hydro projects into single generating systems, and provides decision-support software and expert analysis to ensure optimum system efficiency and reliability.

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ABOVE: Impumelelo substations with boilers and heat pumps in the background. BELOW: The main substation at Impumelelo, a project undertaken by RSV ENCO Hatch Goba Coal JV for Sasol Mining.

CONSTRUCTION WORLD FEBRUARY 2016